Controller of compression-ignition engine

Abstract

A control system for a compression injection engine can prevent deterioration in exhaust purification at the time of the switching of combustion between spark ignition and compression ignition, at the time of said spark ignition combustion and said compression injection combustion, and can diagnose any deterioration of an NO x detector and a three way catalyst. The control system includes a catalytic converter installed within an exhaust passage of the compression ignition engine for compressing and igniting a pre-mixture of a fuel and air, an air/fuel ratio detector for detecting an air/fuel ratio at upstream side of said catalytic converter, and an NO x detector for detecting NO x at downstream side of said catalytic converter.

What is claimed is:  
     
       1. A control system for a compression ignition engine comprising: 
       an ignition coil for igniting a spark;  
       a catalytic converter installed within an exhaust passage of the compression ignition engine, said compression engine functioning in a compression ignition mode and an spark ignition compression mode for compressing and igniting a pre-mixture of a fuel and air;  
       an air/fuel ratio detector for detecting an air/fuel ratio at upstream side of said catalytic converter; and  
       an NO x  detector for detecting NO x  at downstream side of said catalytic converter.  
     
     
       2. A control system for a compression ignition engine as set forth in  claim 1 , wherein said control system uses an output signal of said NO x  detector for preventing deterioration of exhaust gas purification performance. 
     
     
       3. A control system for a compression ignition engine as set forth in  claim 1 , wherein said control system prevents deterioration of exhaust gas purification performance using an output signal of said NO x  detection upon switching transition of combustion mode between said spark ignition mode and said compression ignition mode, during spark ignition mode combustion and during compression ignition mode combustion. 
     
     
       4. A control system for a compression ignition engine as set forth in  claim 1 , wherein said control system further comprises: 
       combustion mode switching means for switching between a spark ignition mode and compression ignition mode;  
       exhaust deterioration factor predicting means for predicting a factor causing deterioration of exhaust gas purification performance on the basis of an NO x  detection value upon switching transition of the combustion mode; and  
       switching learning means for leaning control amount and control object of said combustion mode switching means on the basis of said factor causing deterioration of exhaust gas purification performance.  
     
     
       5. A control system for a compression ignition engine as set forth in  claim 4 , wherein said switching learning means learns a spark ignition timing. 
     
     
       6. A control system for a compression ignition engine as set forth in  claim 4 , wherein said switching learning means learns a throttle valve control amount. 
     
     
       7. A control system for a compression ignition engine as set forth in  claim 4 , wherein said switching learning means learns a fuel injection amount. 
     
     
       8. A control system for a compression ignition engine as set forth in  claim 4 , wherein said switching leaning means learns a fuel cut-off period before switching to said compression ignition mode combustion. 
     
     
       9. A control system for a compression ignition engine as set forth in  claim 4 , wherein said switching learning means learns one of a target intake air flow rate and a target EGR amount. 
     
     
       10. A control system for a compression ignition engine as set forth in  claim 4 , wherein said switching learning means learns an engine operational range for switching combustion mode between said spark ignition mode combustion and said compression ignition mode combustion. 
     
     
       11. A control system for a compression ignition engine as set forth in  claim 1 , wherein said control system performs fuel injection between an expansion stroke and an exhaust stroke in said compression ignition mode combustion. 
     
     
       12. A control system for a compression ignition engine as set forth in  claim 1 , wherein said control system comprises: 
       air/fuel ratio control means for controlling an output of said air/fuel ratio detector toward a target air/fuel ratio;  
       a target air/fuel ratio calculating means for calculating said target air/fuel ratio for optimizing purification ratio of said catalytic converter,  
       said target air/fuel ratio calculating means calculates said target air/fuel ratio on the basis of an output signal of said NO x  detector.  
     
     
       13. A control system for a compression ignition engine as set forth in  claim 12 , wherein said control system temporarily sets said target air/fuel ratio rich side when said NO x  detection value exceeds a predetermined value. 
     
     
       14. A control system for a compression ignition engine as set forth in  claim 1 , wherein said control system comprises NO x  detector diagnosis means for diagnosing abnormality of said NO x  detector for controlling the air/fuel ratio so that an output of said air-fuel ratio detector becomes stoichiometric value. 
     
     
       15. A control system for a compression ignition engine as set forth in  claim 1 , wherein said control system comprises combustion deterioration detecting means for detecting deterioration of combustion on the basis of an NO x  detection value in said compression ignition mode combustion. 
     
     
       16. A control system for a compression ignition engine as set forth in  claim 15 , wherein said combustion deterioration detecting means detects deterioration of combustion in said compression ignition mode combustion when an output of said air/fuel ratio detector indicates a lean mixture condition. 
     
     
       17. A control system for a compression ignition engine as set forth in  claim 15 , wherein said control system comprises combustion improvement control means for controlling improvement of combustion in said compression ignition mode when deterioration of combustion is detected by said combustion deterioration detecting means. 
     
     
       18. A control system for a compression ignition engine as set forth in  claim 17 , wherein said control system controls the air/fuel ratio so that the output of said air/fuel ratio detector becomes stoichiometric value when deterioration of combustion is detected by said exhaust deterioration detecting means after implementation of said combustion improvement control means. 
     
     
       19. A control system for a compression ignition engine as set forth in  claim 1 , wherein said control system comprises air/fuel ratio detector diagnosing means for detecting abnormality of said air/fuel ratio detector, for correcting a fuel injection amount on the basis of said output signal of said NO x  detector when abnormality of said air/fuel ratio detector is detected. 
     
     
       20. A control system for a compression ignition engine as set forth in  claim 1 , wherein said control system prevents deterioration of exhaust gas purification performance by detecting fatigue of at least one of said NO x  detector and said catalytic converter. 
     
     
       21. A control system for a compression ignition engine as set forth in  claim 20 , wherein said control system comprises fuel cut-off means for interrupting fuel injection during deceleration, and fatigue of NO x  detector is detected on the basis of the output signal of said NO x  detector during fuel cut-off. 
     
     
       22. A control system for a compression ignition engine as set forth in  claim 21 , wherein said control system comprises fuel recovery means for recovering fuel injection after fuel cut-off, abnormality of said NO x  detector is judged when a difference said NO x  detection value during fuel recovery and said NO x  detection value during fuel cut-off is less than or equal to a predetermined value. 
     
     
       23. A control system for a compression ignition engine as set forth in  claim 20 , wherein said control system comprises air/fuel ratio control means for controlling air/fuel ratio so that an output of said air/fuel ratio detector becomes close to a target air/fuel ratio, for diagnosis of fatigue of said catalytic converter on the basis of the output signal of said NO x  detector when said target air/fuel ratio is set at stoichiometric value. 
     
     
       24. An automotive vehicle having a control system for a compression ignition engine defined in  claim 1 .